The present invention relates to a method for the control of a brake-slip controlled brake system for automotive vehicles, in particular for road vehicles, wherein the pedal force assisted by auxiliary force is transmitted onto a master cylinder and is therefrom transmitted onto the individual wheel brake cylinders via several pressure fluid paths adapted to be closed independently of one another, and wherein the wheel rotational behavior and the vehicle velocity or a value corresponding to the vehicle velocity will be measured, the signals obtained thereby will be logically combined and processed as well as evacuated to generate control signals by which in the event of a control action, i.e. upon the occurence of an imminent locked condition at a wheel, the braking pressure at the wheels will be decreased, kept constant or increased individually or in groups in dependence upon the wheel rotational behaviour. Brake systems for implementing this method are likewise covered by the present invention.
As used herein, the word "dose" means a force which is applied during the period of a pulse which recurs cyclically at a pulse repetition frequency governed by the instantaneous wheel rotational behavior.
There are known already brake-slip controlled brake systems, wherein the auxiliary energy for boosting the brake pedal force acting on the master cylinder is developed by virtue of a hydraulic unit which is substantially composed of an electromotively driven pump and a hydraulic accumulator. In this arrangement, there is assigned to each individually controllable wheel one electromagnetically actuatable inlet valve that is inserted in the path connecting the master cylinder to the wheel cylinder. Moreover, the wheel brake cylinder may be connected to the supply reservoir via an outlet valve. If both valves are `closed`, the braking pressure at the connected wheel remains constant. If the outlet valve is opened for a short time, in dependence upon the magnitude of the pressure level desired, discharge of pressure medium to the supply reservoir and thus pressure decrease will take place. Therefore, a re-increase of the braking pressure by renewed opening of the inlet valve would have as a result a reduction of the hydraulic volume in the working chamber of the master cylinder and finally an exhaustion, for what reason pressure medium has to be supplied to the working chamber via a separate path with the aid of the auxiliary energy source (German printed and published patent applications Nos. DE-OS 30 40 561, DE-OS 30 40 562).
In other known brake systems comprising hydraulic energy supply, the master cylinder will be isolated temporarily from the hydraulic brake circuit of the controlled wheel by means of switching valves during control actions, and the volume discharged into the supply reservoir during pressure decrease will be topped up directly out of the auxiliary energy source (German Pat. No. 21 37 904).
It is also known to pump the brake fluid removed from the wheel brake cylinder during pressure decrease back into the master cylinder by means of a return delivery pump (Bosch, Technische Berichte, volume 7 (1980), edition 2, page 87).
The supply of fluid into the working chambers of the master cylinder or - by circumventing the master cylinder--directly into the wheel brake cylinder involves in all cases relatively great manufacturing efforts.
Other known brake slip control systems are equipped both with a vacuum power brake booster and with a hydraulic unit as auxiliary energy source for the event of control action (German printed and published patent application No. 30 10 639). This bears the advantage that, upon failure of the hydraulic unit, the brake force boosting--via the vacuum booster--is maintained. The expenditure entailed in total is, however, considerable.
The quantity of fluid taken from the wheel brake cylinder for the purpose of braking pressure decrease may principally be received also in a plunger chamber, that means a cylinder chamber closed by a piston (German printed and published patent application No. 31 19 144). In this case, for re-build-up of the pressure, the plunger chamber will be narrowed by resetting of the piston by the action of an auxiliary force, as a result whereof the fluid propagates back to the wheel brake cylinder. Likewise such brake systems involve much effort.
It is therefore an object of the present invention to develop a reliable brake slip control apparatus which meets all requirements and which distinguishes over known brake systems of this type above all by a straightforward design and by requiring little manufacturing efforts.